1. Statement of the Technical Field
The inventive arrangements relate generally to methods and apparatus for providing increased design flexibility for RF circuits, and more particularly to tunable waveguide filters.
2. Description of the Related Art
Waveguide filters are known to those skilled in the art of microwave communications. Waveguide filters commonly include a plurality of adjacently positioned waveguide cavities separated by shunt inductive reactance elements. The shunt inductive reactance elements are typically inductive posts which connect the broad walls of a waveguide, or openings through which adjacent cavities are coupled. For example, in a corrugated resonator configuration a slot opening is provided. In an iris configuration, a circular opening is provided. In operation, each of the waveguide cavities resonate at a frequency which is determined by cavity dimensions and the velocity of electromagnetic fields within the cavities.
In a tunable waveguide the frequency at which the cavities resonate can be adjusted. For example, in one arrangement tuning screws protrude into each waveguide cavity to adjust the waveguide filter down in frequency. As the screws protrude further into the cavity, the frequency is adjusted lower. The adjustment of a waveguide filter incorporating tunings screws is a manual process and usually only adjusts the waveguide filter by a few percentage points. Since each waveguide filter cavity has its own screw, the adjustment of such a tunable waveguide filter can be a time consuming and tedious process.
In another arrangement, dielectrically loaded waveguide filter includes two ceramic disks located on top of each other in each waveguide filter cavity. For each disk pair, a first moveable disk is connected to a stepping motor which moves the first disk with respect to a second disk. This configuration provides a tuning range of proximately 18%, but it is also very sensitive to imperfections in the ceramic disks which adversely affect waveguide filter performance. To compensate for this sensitivity, a dedicated stepping motor and drive assembly is required for each waveguide filter section. Further, the position of the movable disk in each disk pair must be individually adjusted using a complex algorithm to drive the stepper motors. Such a waveguide filter implementation is very expensive and physically large.